1. Field of the Invention
This invention relates to novel cellulose ester derivatives and a process for the production thereof. More specifically, it relates to cellulose ester derivatives useful for various uses such as coating agents, thickening agents etc.
2. Description of the Prior Art
Cellulose esters such as cellulose nitrate, cellulose acetate, cellulose propionate etc. are soluble in various solvents and are good in compatibility and miscibility with plasticizers and other polymers, and many of them exhibit thermoplastic properties by employing plasticizers, and therefore they are widely employed as molded products, fibers, coating agents etc. For producing these cellulose esters, it is general to react cellulose with an acid, an acid anhydride, an acid halide or the like employed as an esterifying agent. However, there has hitherto been known hardly any useful one which employs a lactone as an esterifying agent. Especially in this case, since the product is the one having free hydroxyl groups, i.e. a hydroxyalkyl ester of cellulose, it is expected to exhibit physical properties different from those of the aforesaid alkyl esters or inorganic acid esters of cellulose, and novel uses, for example, uses utilizing compatibility with hydrophilic polymers, are expected.
In this respect, for example, R. M. Reinhardt 5 [Text. Res. J. 26, 1 (1956)] obtained an esterified cotton fiber having improved resistance to microorganisms, felting properties, dyeing properties etc. by treating cotton with an alkali and .beta.-propiolactone. However, this reaction production was not reported as being soluble in solvents. Furthermore, under these reaction conditions, a large amount of a homopolymer of .beta.-propiolactone itself (ring opening polymerization) was obtained as a by-product.
The present inventors have been successful in efficiently effecting the esterification of cellulose by appropriately selecting the lactone as the esterifying agent and the reaction conditions, and have confirmed that they should be novel cellulose esters by solubilities, infrared spectra, NMR spectra etc., thereby having accomplished this invention.
One of the features of this invention is that novel compounds have been obtained by employing specific lactones such as glycolide, lactide or .epsilon.-caprolactone which is relatively poor in autogenous ring opening polymerizability as an esterifying agent. The aforesaid lactones poor in autogenous ring opening polymerizability are, in other words, the accordingly stable compounds, and thus they are also poor in esterification reactivity. The present inventors have succeeded in the esterification reaction with specific lactones by conducting the esterification reaction of cellulose in a uniform solvent system.
Japanese Patent Application Laid-Open No. 32501/1981 described a method for dissolving cellulose in N,N-dimethylacetamide, N-methyl-2-pyrrolidone or a mixture thereof in the presence of lithium chloride. The present inventors have further discovered that cellulose is also soluble in a mixture of lithium chloride and 1,3-dimethyl-2-imidazolidinone. One of the other features of this invention is that cellulose and a lactone are reacted in the aforesaid solvent system also in the presence of a basic compound. It has been observed that the reaction of this invention proceeds under relatively mild conditions and the product is completely soluble in water and in several hydrophilic organic solvents.